1. Field of the Invention
The present invention relates to an indexing apparatus having a plurality of work platens or pallets movable through successive workstations. More particularly, the present invention relates to methods and apparatus for safely coupling the platens to a drive assembly during operation of the apparatus. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Related Art
It is known in the indexer art that endless conveyors containing a plurality of platforms (also described herein as platens or pallets) can be used to move workpieces on the platens through the various workstations. It is also known to use such apparatus in the screen printing art. However, problems with multi-color printers of the related art arise from the fact that such printers have a fixed configuration with a fixed number of printing stations printing a fixed number of colors. If additional colors are to be printed, the workpieces, in the typical case a print substrate, must be run through the same or a different printer having the additional colors. This greatly limits productivity.
Other deficiencies associated with indexing apparatus used with printers of the related art result from the shear size and massiveness of the related art printing apparatus. In particular, it is noted that printing apparatus of this type can be almost 40 feet long and weigh on the order of 20,000 pounds. The sheer size and weight of such apparatus give rise to the danger that the apparatus operators can be seriously injured due to (1) equipment failure; (2) the inadvertent introduction of foreign objects into the apparatus; and/or (3) partial or complete entrapment in the apparatus. Moreover, even minor malfunctions of such machinery can lead to operator injury and/or additional damage to the apparatus itself. For example, decoupling of the platens from the drive assembly in a conventional indexer can easily lead to a "pile-up" of platens before the apparatus can be manually shut-down.
Traditionally, efforts to reduce or eliminate such dangers have focused the use of shear pins which mechanically couple the platens and the associated drive assembly. Basically, such shear pins provide a replaceable "weak link" in the system so that the damage caused by many apparatus failures will be limited to breakage of the shear pin. For example, inadvertent placement of a foreign object into the path of the platens will merely stop movement of the platen and break the shear pin. Since such a foreign object may be an operator's appendage, use of the shear pin may very well save the operator from serious injury.
The shear pin arrangements of the related art, however, suffer from many deficiencies. First, each time a shear pin serves its purpose of preventing substantial damage, the shear pin must be replaced. Depending on the particular circumstances, this may entail an extensive, expensive and lengthy procedure. Naturally, in the event that the shear pin breaks due to a very minor malfunction, the cost of replacing the shear pin can greatly exceed the damage which the shear pin actually prevented. Second, conventional shear pin arrangements cannot prevent damage resulting from a "pile-up" of platens once one shear pin has broken. In other words, indexing apparatus of the type discussed herein tend to be subjected to a "domino effect" once damage begins to occur. Conventional shear pin arrangements simply lack the ability to prevent consequential damage of this sort. Thus, conventional procedures require an operator to manually shut the apparatus down. This, however, requires a relatively long period of time during which simply unnecessary damage often occurs.
Accordingly, there remains a need in the art for improved indexing apparatus for use with a multi-station apparatus which can be combined, broken apart and reconfigured as desired while still providing a fast and effective safety mechanism for minimizing operator injury as well as damage to the apparatus itself.
There remains a further need in the art for an indexing apparatus which employs an improved safety coupling assembly which is capable of quickly and automatically shutting-down the apparatus in the event of a malfunction or operator injury.
There remains still another need in the art for an indexing apparatus utilizing an improved indexing apparatus which is capable of long term repeated use without suffering significant degradation in performance.
There is yet another need in the art for an improved indexing apparatus which prevents unnecessary consequential damage to the apparatus by eliminating further advancement of the platens in the event of apparatus failure.